Various types of electronic equipment including digital computers are frequently used in worldwide environments where readily available input power is different in different countries. For example, in the United States power at 115 volts is readily available and in Europe 230 volts is common. Such equipment must convert the readily available ac power to the constant voltage dc power required by electronic circuits. That function is provided by a rectifier apparatus, often called a power supply, connected between the ac power line and the dc power distribution system supplying the electronic circuits.
To accommodate a factor of two in the range of possible ac input voltage levels and still provide essentially the same dc output voltage level, it has become increasingly common in power supply design to provide a full-wave bridge rectifier for a high voltage input and a voltage-doubler rectifier for a low voltage input, the appropriate configuration selected by a switch. The selected rectifier is often followed by a high-frequency dc to dc converter for providing the desired output voltage levels from input voltage ranges exceeding the aforementioned factor of two.
Another frequently used method of accommodating wide ranges of input voltage is the boost rectifier where energy is stored in an inductor when a switch is closed and the stored energy is transferred through a diode to a capacitor when the switch is opened. By operating the switch at a high frequency relative to the line voltage frequency and with a programmed duty cycle, the dc output voltage supplied to a load can be regulated and in addition the ac line power factor can be corrected as required.
However, in commonly used high frequency boost rectifiers, the inductor has conflicting requirements. First, it must have an inductance value sufficiently large for the highest line voltage when the current requirement is low. Second, it must have current capacity sufficient for the lowest line voltage when the inductance requirement is low. These conflicting requirements result in an inductor that is more expensive and physically larger than that needed for either the high or low line voltage case alone.
It is an object of the invention to provide a circuit configuration that reduces the peak current requirements on inductors used in boost rectifiers.
Also, in conventional boost rectifiers, the output circuit diodes and transistors, which are high speed switching devices, must withstand voltages at least as high as the highest value of the peak ac input voltage. As a consequence, because high voltage devices tend to be slower and to have higher resistance than otherwise equivalent low voltage devices, semiconductor costs or power dissipation (or both) tend to be high.
It is an additional object of the invention to provide an output circuit configuration in which the semiconductor switching devices are exposed to voltages much lower than the output voltage resulting in lower costs and improved performance and reliability.